The present invention relates to a photocurable resin composition used in three dimensional photofabrication, a process for making a three-dimensional object and the resulting three-dimensional object.
In recent years, photofabrication of three-dimensional objects made from cured resin layers integrally laminated by repeating a step of selectively irradiating a photocurable resin composition has been proposed (see Japanese Patent Application Laid-open No. 247515/1985, U.S. Pat. No. 4,576,330 (Japanese Patent Application Laid-open No. 35966/1987), Japanese Patent Application Laid-open No. 101408/1987, and Japanese Patent Application Laid-open No 24119/1993).
A typical example of such photofabrication is as follows. The surface of a photocurable resin composition (a liquid material) in a vessel is selectively irradiated with light from an ultraviolet laser and the like based on CAD data to form a cured resin layer having a specified pattern. The equivalent of one layer of a resin composition is provided over this cured resin layer and the liquid surface is selectively irradiated to form a new cured resin layer integrally laminated over the cured resin layer. This step is repeated a certain number of times using the same or different irradiating patterns to obtain a three-dimensional object consisting of integrally laminated cured resin layers. The object preferably is washed with a washing agent to remove excess resin sticking to the surface of the object, and the object preferably is postcured by for example UV or heat to further improve the mechanical properties of the object. This photofabrication has attracted considerable attention because a three-dimensional object having a complicated shape can be easily formed in a short period of time.
The prior art discloses a number of resin compositions that can be used for this process. Examples of photocurable resin composition used in the photofabrication of three-dimensional objects are the following resin compositions (1) to (4).
(1) A resin composition comprising a radically polymerizable organic compound such as urethane (meth)acrylate, oligoester (meth)acrylate, epoxy (meth)acrylate, thiol compound, ene compound, and photosensitive polyimide (see, for example, Japanese Patent Applications Laid-open Nos. 204915/1989, 208305/1990, and 160013/1991).
(2) A resin composition comprising a cationically polymerizable organic compound such as an epoxy compound, cyclic ether compound, cyclic lactone compound, cyclic acetal compound, cyclic thioether compound, spiro orthoester compound, and vinyl ether compound (see, for example, Japanese Patent Application Laid-open No. 213304/1989).
(3) A resin composition comprising both a radically polymerizable organic compound and a cationically polymerizable organic compound (see, for example, Japanese Patent Applications Laid-open Nos. 28261/1990, 75618/1990, and 228413/1994).
(4) A resin composition comprising a cationically polymerizable organic compound, a radically polymerizable organic compound (an ethylenically unsaturated monomer), a polyether, polyol compound, and elastomer particles (see, for example, Japanese Patent Application Laid-open No. 310626/1999.
A number of problems exists with the resin compositions disclosed in the prior art or with the application of these resin compositions in a process for making three dimensional objects. One problem with conventionally known resin compositions such as the above resins (1) to (4) is formation of bubbles when the resin composition is supplied onto a cured resin layer (by a coating operation or leveling operation by means of squeezing) or when the resin composition is circulated by a pump or agitated in a container. The bubbles may remain in the formed three-dimensional articles without being destroyed.
The bubbles remaining in the formed three-dimensional articles do not only impair external appearance of the three-dimensional articles, but also remarkably weaken the mechanical strength because the stress is concentrated in the area where the bubbles are present.
Addition of a silicone compound to the resin composition can be one way of overcoming the problem of formation and existence of bubbles. The silicone compound may decrease the surface tension of the resin composition and may destroy the bubbles.
However, a resin composition comprising a compound having an effect of destroying bubbles such as a silicone compound (hereinafter referred to as xe2x80x9cdefoaming agentxe2x80x9d) may cause uneven coating when supplied (coated) onto a cured resin layer due to repelling. It is impossible to obtain a uniform thin coating layer on the surface of a cured resin layer using such a resin composition.
No resin compositions which can form three-dimensional articles free from remaining bubbles and exhibits excellent coatability have conventionally been known.
Another problem of the compositions of the prior art is that they tend to absorb water depending on the specific conditions of the environment. Absorption of water may have large consequences for for example viscosity of the resin and thereby for the process of making the three dimensional objects.
Another problem of the compositions and process known in the art is the application of washing agents to remove excessive solvent. Washing agents like for example ethanol tend to be absorbed into the object, causing swelling and deformation of the object and a significantly decrease of the strength of the photofabricated product. Such phenomena tend to occur especially when the photofabricated product is washed with a thin portion of solvent.
The disadvantage of absorption of solvent by the three-dimensional object is especially pronounced when the objects are treated that have a high rubber elasticity. Examples of compositions that may be used to make such objects having high rubber elasticity can be found in for example Japanese Patent Application No. 97433/1999 and No. 165103/1999, which are incorporated herein by reference. The present inventors have found that liquid resins adhering to the surface of a photofabricated product cannot be completely removed using a washing agent containing water as a major component (see Japanese Patent Application No. 111529/1990). This is because liquid resins cannot be dissolved or dispersed in a washing agent containing water as a major component.
As described above, a washing agent which causes a photofabricated product (cured resin) to swell to a very low degree and exhibits good washing performance for liquid resins (uncured resins) has not yet been proposed.
The present invention has been achieved in view of the above situation.
A first object or the present invention is to provide a photocurable resin composition suitable for use in a stereolithography process in which the bubbles produced during handling or processing of the resin composition are destroyed in a short period of time and which not only can form a three-dimensional object free from residual bubbles, but also exhibits excellent coatability without repelling (without producing defective coating) and can form a uniform thin coating layer on the surface of the cured resin layer.
A second object of the present invention is to provide a three-dimensional object containing no residual bubbles, exhibiting superior external appearance, and possessing excellent mechanical strength.
A further object of the present invention is to provide a photocurable resin composition which can be fabricated into three-dimensional objects with desired properties (interlayer adhesion and fabrication accuracy) under the constant fabricating conditions in a stable manner without any substantial change in the fabricating characteristics (curing depth) after having been stored for a long time under normal use conditions (10-30xc2x0 C., 20-80% RH).
Still another object of the present invention is to provide an improved stereolithography process which uses in a washing step a washing agent which is capable of completely removing uncured liquid resins adhering to the surface of a photofabricated product and which washing agent neither causes the photofabricated product to be deformed nor decreases the strength of the photofabricated product.
As a result of extensive studies to achieve the above objects, the inventors of the present invention have found that a photocurable resin composition prepared by adding a copolymer, which is obtained by copolymerizing specific (meth)acrylate monomers, to a resin composition containing a cationically polymerizable organic compound and a cationic photoinitiator, as essential components, exhibits excellent coatability and can produce three-dimensional objects which are free from residual bubbles.
The resin composition of the present invention used in three-dimensional photofabrication comprises: (A) a cationically polymerizable organic compound, (B) a cationic photoinitiator, and (C) a (co)polymer obtainable by (co)polymerization of monomers comprising at least one (meth)acrylate-group comprising monomer.
The (co)polymer of the component (C) includes homopolymers obtainable of a single (meth)acrylate-group containing monomer, copolymers obtainable from two or more (meth)acrylates-group containing monomers, and copolymers made from one or more (meth)acrylates-group containing monomers and one or more other monomers that are copolymerizable with the (meth)acrylate-group containing monomer(s).